<!DOCTYPE html>  
<html>  
<head>  
    <meta charset="utf-8">  
    <title>JS实现文件上传下载</title>  
</head>  
<body>  
<a href="javascript:void(0);" id="oDownLoad" onclick="oDownLoad('111.jpg','oDownLoad')">下载</a>
<a href="javascript:void(0);"></a>  
</body>  
<script>  
//这行注释是拿来试一次的
    function myBrowser(){  
        var userAgent = navigator.userAgent; //取得浏览器的userAgent字符串  
        var isOpera = userAgent.indexOf("Opera") > -1;  
        if (isOpera) {  
            return "Opera"  
        }; //判断是否Opera浏览器  
        if (userAgent.indexOf("Firefox") > -1) {  
            return "FF";  
        } //判断是否Firefox浏览器  
        if (userAgent.indexOf("Chrome") > -1){  
            return "Chrome";  
        }  
        if (userAgent.indexOf("Safari") > -1) {  
            return "Safari";  
        } //判断是否Safari浏览器  
        if (userAgent.indexOf("compatible") > -1 && userAgent.indexOf("MSIE") > -1 && !isOpera) {  
            return "IE";  
        }; //判断是否IE浏览器  
        if (userAgent.indexOf("Trident") > -1) {  
            return "Edge";  
        } //判断是否Edge浏览器  
    }  
  
    function oDownLoad(url,id) {  
        if (myBrowser()==="IE" || myBrowser()==="Edge"){  
            var oPop = window.open(url,"","width=1, height=1, top=5000, left=5000");  
            for(; oPop.document.readyState != "complete"; )  
            {  
                if (oPop.document.readyState == "complete")break;  
            }  
            oPop.document.execCommand("SaveAs");  
            oPop.close();  
        }else{  
            //!IE  
            var odownLoad=document.getElementById(id);  
            odownLoad.href=url;  
            odownLoad.download="";  
        }  
    }  
</script>  
</html> 